Apparatus and method for governing the operation of down- hole earth boring motors

ABSTRACT

Apparatus and method for governing the operation of down-hole earth boring motors in which braking forces are applied to a rotating drill string in accordance with the reactive torque generated in the drill string by the down-hole motor driving the drill bit, the weight load on the drill bit being varied in accordance with variations in the speed of drill string rotation.

United States Patent Clark [54] APPARATUS AND METHOD FOR GOVERNING THE OPERATION OF DOWN- HOLE EARTH BORING MOTORS Wallace Clark, 1830 S. German Church Road, Indianapolis, Ind. 46239 Filed: Oct. 23, 1970 App]. No.: 83,455

Inventor:

US. Cl. ..l75/26, 175/27, 175/57 Int. Cl. .....E2lb 3/08, E2lb 7/00 Field of Search 175/26, 27, 57

References Cited UNITEDSTATES PATENTS 1,786,173 12/1930 Scharpenberg ..l75/26 [15] 3,675,727 [451 July 11,1972

1,703,234 2/1929 l-iallibarton 175/27 3,550,697 12/1970 Hobhouse 175/26 1,935,105 11/1933 Woollen ..l75/26 Primary Examiner-James A. Leppink Attorney-Melville, Strasser, Foster & Hoffman [57] ABSTRACT Apparatus and method for governing the operation of down hole earth boring motors in which braking forces are applied to a rotating drill string in accordance with the reactive torque generated in the drill string by the down-hole motor driving the drill bit, the weight load on the drill bit being varied in accordance with variations in the speed of drill suing rotation.

12 Claims,5DrawingFlgures PATENTEDJUL 11 1972 3. s75 727 sum 1 2 Fin 1 INVENTORIS 4 WALLACE CLARK ATTORNEYS APPARATUS AND METHOD FOR GOVERNING THE OPERATION OF DOWN- HOLE EARTH BORING MOTORS BACKGROUND OF THE INVENTION This invention relates to well drilling apparatus and a method of drilling wells utilizing a rotary drilling rig in which the drill bit is driven by means of a motor mounted at the bottom of the drill string. Such down-hole earth boring motors are constructed to be powered hydraulically, electrically or penumatically. I-lydraulically powered motors are the most prevalent, the motor being driven by a fluid, such as mud, which is pumped through the drill pipe from a reservoir by means of a pump set to deliver the mud at the required rate of flow. The drill bit motor, if rotating a drilling bit in a clockwise direction, will cause the drill string to reactively rotate in a counterclockwise direction, and it is customary to hold the drill string against such rotation by means of a conventional rotary table mounted on the drilling rig at the top of the hole. It has also been the practice to slowly rotate the drill string in the direction of rotation of the drill bit, thereby overcoming the reactive torque created by the motor in order to prevent mud channeling and to assist in maintaining straightness of the hole. This is normally done by driving the rotary table, which is operatively connected to the drill string by means of a kelly extending through the rotary table, the kelly rotating with the table and hence rotating the attached drill string.

In drilling a hole, such as a well, especially when using a down-hole motor, it is desirable that the drilling be accomplished with optimum performance of all equipment, but within the capacities of the equipment and with the least possible wear. The down-hole motor and drill bit represent the major items of cost in day-to-day drilling operations, and consequently it is desirable to operate the equipment so as to obtain maximum useful life of the motor and bit. Both the high cost of the equipment and the labor required to perform the drilling operation dictates that the operator endeavor to achieve optimum rate of penetration into the earth. Because of these factors, the operator pushes the equipment as much as he dares, but since he cannot see the motor or the drill bit which may be miles away in a deep well his customary guide for operation is the pressure gauge on the line supplying fluid to drive the down-hole motor. The operator must determine whether he is allowing the draw works from which the drill string is suspended to relax sufficiently to provide sufficient weight on the drill bit so that it will penetrate at the optimum rate. Optimum does not necessarily mean maximum, for if too much weight is let down the bit will stall, and if the formation encountered by the bit is soft, it may ball-up the bit or choke the annulus through which the driving fluid is discharged, thus impeding the return circulation of the fluid upon which the cleansing of the hole depends. In addition, the fluid pressure often runs up to excess and can readily damage the motor. Consequently, the operator, if carefully watching the pressure indicator, will at best attempt to raise the string quickly before damage is incurred. However, he is often too late because of other duties which must be performed, fatigue, or errors in judgment. Upon the stalling of the bit, the operator must raise the entire weight of the string (which may be several hundred tons or more) in order to let the motor recover its normal speed, while at the same time hoping that the motor does not over-speed under no-load conditions and hence run further risk of damage.

As the drill hole deepens, the operator must use higher fluid pressures to overcome the internal friction of the fluid as it travels down the drill string and up the annulus, such friction increasing with each addition to the length of the drill string. The operator has no dependable method for determining the fluid pressure drop through the down-hole motor and must rely on calculations made by reference to fluid friction tables which only apply to the system as a whole. Fearing a stall, he cannot reduce the volume of flow from the fluid pump since such reduction of flow might result in the hole being further clogged from lack of adequate washing of the cuttings and lack of power at the drill bit. The difl'ieulties resulting from falling volume of fluid, whether by design or conditions in the hole, are cumulative, including the rebuilding of excessive pressure. Consequently, the only thing the operator can do to prevent a stall, or recover from one, is to come off bottom with the drill string, which procedure may in itself create additional problems, such as over speeding and time loss.

In contrast to the procedures which have hitherto been followed, inclusive of those taught in U.S. Pat. No. 3,043,380, dated July 10, 1962 and entitled Means For Governing Fluid Pump In Rotary Well Drilling Rig", which seeks to control the speed of rotation of the drill bit in accordance with fluid pressure, the instant invention contemplates apparatus and procedures which afford the operator new and enhanced parameters of control based on the reactive torque developed in the drill string by the drill bit motor under varying conditions encountered during the drilling operation.

RESUME OF THE INVENTION In accordance with the invention, the drill string is permitted to rotate slowly or is releasably held against rotation by a braking device operatively connected to the drill string, such braking device acting to control the effect of the reactive torque developed in the drill string by the drill bit motor. In one embodiment of the invention, the braking device will engage a bushing mounted on the normally used kelly, the kelly extending through and engaging the conventional rotary table, but the table will be free to rotate in the reverse direction to the direction of rotation of the drill bit. The braking mechanism preferably will be supported by a clamp arm which is in turn supported by cables from above in the manner of a pipe tong generally present on the rig and used to connect and disconnect the various sections of the drill string. Altematively the braking mechanisms may rest on the rotary table, or, for safety, it may be supported just above the table so as not to interfere with motion of the rotary table. The braking mechanism will be suitably anchored to the rig to fix it against movement with the drill string.

In another embodiment of the invention, the braking device will be operatively connected to the rotary table itself. Itrespective of its location, the braking mechanism may take numerous forms and may be actuated mechanically, electrically, hydraulically or pneumatically. Preferably, the braking mechanism will be hydraulically controlled, the operator's console being provided with suitable hydraulic lines and valving enabling the operator to adjust the braking force applied to the drill string. The mud used to drive the down-hole motor also may be utilized to control the braking mechanism in several modifications of the invention; and the braking mechanism itself may comprise a helical gear pump utilized as a brake.

In the operation of the equipment and to obtain optimum drilling, the operator will establish a nearly stationary condition of the drill string by setting the brake and balancing the drilling by relaxing the drill string supporting cables so as to put as much weight on the drill bit as possible without stalling it. With the motor just under the stalling point, the operator makes certain that the brake is set so as to just barely hold the drill string from turning or, preferably, allowing the drill string to turn slowly in the reverse direction. If there is a change in the formation encountered by the bit, as for example upon entering a softer formation, the operator will be alerted by an increase in speed of rotation of the rotary table as the torque on the drill string is increased and the holding or retarding force of the brake is overcome. However, the bit will not stall since it will be efiectively slowing down in ground speed as the rotational speed of the drill string increases. With a loose brake the drill string will rotate reversely and its speed will be in inverse proportion to the bit speed, except for minor effects due to opposing frictional loads. However, in slowing down, the bit is not backing up cuttings in the hole for lack of fluid flow and thus plugging the hole, because the brake slippage acts to relieve the back pressure and the fluid flow is maintained even though the rotational ground speed of the bit and the penetration is slower. The. operator can then balance the system by lightening the weight on the bit without having to come all the way off bottom, whereupon he may readjust the brake to slow the rotation of the drill string while watching the pressure gauge. If he finds that as the string slows down the fluid pressure tends to rise excessively, this indicates that he must further lighten the weight on the bit. By corrective adjustment of the weight load on the bit he can readily establish as much weight on the bit as the down-hole motor is capable of handling in the particular formation. If, on the other hand, the bit strikes a hard area which will permit the bit to rotate at a higher rate of speed, this will result in less reactive torque in the drill string which will be indicated by a slowing clown or stoppage of its rotation. The operator can readily increase the weight on the bit by lowering the drill string and therefore drill faster, again balancing by adjusting the brake to a new setting, if necessary.

DESCRIPTION OF THE DRAWING ized in conjunction with the braking mechanism of FIG. 3.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 illustrates an exemplary rotary drilling rig comprising a string of drill pipe 1 extending downwardly into a well 2, the drill pipe mounting adjacent its lowermost end a drill bit motor 3 which acts to rotate the drill bit 4. Preferably, a hydraulic drill bit motor will be employed, reference being made to U.S. Pat. No. 2,898,087, dated Aug. 5, 1959 and entitled Well Drilling Apparatus And Method", wherein a drill bit motor and bit assembly capable of use in conjunction with the instant invention is disclosed.

At its upper end the string of drill pipe is fixedly secured to a polygonal kelly 5 which is slidably journaled in a rotary table 6, the kelly projecting upwardly beyond the rotary table where it is suspended by book 7 forming a part of the draw works 8 suspended from the rig, a portion of which is indicated at 9, the draw works enabling the operator to raise and lower the drill string.

At its uppermost end, the kelly mounts a swivel connection 10 to which a fluid supply hose 11 is connected through which the drilling fluid is supplied to the drill string by means of pump 12 arranged to withdraw the drilling fluid from a supply source 13, which may comprise drilling mud recovered from the drilling operation. It will be understood that the kelly 5 is hollow so that the fluid will flow downwardly therethrough into the drill string and to the motor 3, the fluid then flowing outwardly through the drill bit and thence upwardly within the annulus of the drill hole from which it is evacuated and normally returned to the supply source 13 by means which will be readilyunderstood by the worker in the art, such means being diagrammatically indicated at 134.

While in accordance with the invention, the rotary table 6 is free to rotate in the reverse direction to the drill bit, some conventional disengageable drive means, represented by the bevel gear 14, is normally provided to drive the table when so desired. For example, the operator may wish to rotate the drill string at times when the braking means is not in use. With the arrangement just described, the down-hole motor 3 drives the kelly 5 through the drill string 1, and in turn the kelly drives the rotary table reversely to the direction of rotation of the bit.

In accordance with one embodiment of the invention, the kelly is provided with a bushing 15 which moves freely up and down on the kelly, just as the kelly moves freely relative to the ordinary kelly bushing used to connect the rotary table to the kelly. As seen in FIG. 2, the bushing 15 may have an annular I device in the nature of a drill pipe tong capable of being adjusted to vary the braking force applied to the bushing and hence to the kelly and drill string. The braking mechanism 18 is provided with a hanger 19 by means of which it is suspended from a cable 20 secured to the rig, the jaws 18a and 18b permitting the braking mechanism to be removed easily using the hanger and cable. A cable 21 having suitable tightening means 22 secures the braking mechanism to a mast leg of the rig, thereby preventing the braking mechanism from rotating with the kelly. It will be understood, of course, that other support means may be provided for the braking mechanism, although the arrangement disclosed is preferred, particularly if the braking mechanism is also employed as a tong for connecting and disconnecting the pipe sections.

The braking mechanism may be hydraulically controlled, as by means of hydraulic pump 23 which pumps hydraulic fluid from supply tank 24 through hose 25 to the braking mechanism 18, the hose 26 serving to return the fluid to the supply tank 24. Preferably a pressure control valve 27 will be provided by means of which the operator may adjust and set the grip of the brake shoes 17 or other gripping means at the required strength. It is to be understood that the valving means may be remotely located or remotely controlled, as where it would be placed at the driller's station. Such valving means also may be used to relieve excessive fluidpressure by passing fluid to the return hose 26 instead of having it flow to the hydraulic cylinder or the like utilized to actuate the clamping jaws or brake shoes which engage the bushing on the kelly. While it is convenient to utilize the rotary means for indicating variations in drill string torque, the braking mechanism may be provided with a torque indicator 28 which will also give a visual indication of changing conditions encountered by the drill bit.

As should now be evident, the braking mechanism provides a means to efiectively hold the drill string against rotation, and by adjusting the braking force applied to the kelly, the drill string may be permitted to rotate very slowly. As should also be evident, if the drill string were permitted to rotate freely, it would result in complete inactivity of the drill bit. However, by effectively holding the drill string against reverse rotation, the full force of the driving fluid will be utilized to drive the drill bit, thereby achieving maximum power. Thus, optimum penetration can be achieved by lowering the drill string to increase the weight load on the bit until it is just short of the point at which the bit will stall.

In instances where the bit subsequently encounters greater resistance, as for example upon entering a softer formation, the reactive torque exerted on the drill string will increase and will overcome the holding force of the brake, thereby increasing the speed of rotation of the rotary table and giving visible notice to the operator that adjustment is required. The operator will make the necessary adjustment by lightening the weight load on the drill bit, but in so doing he does not have to lift the bit completely off bottom. Rather, he can gradually lift the drill string until rotation of die table has slowed down, evidencing that the holding force of the braking means has table as a visual again taken over, or he can readjust the braking means to slow the rotation of the table while watching the pressure gauge on the fluid pump to be certain that the pressure does not unduly rise, which would indicate that the bit was again approaching the stalling point.

Conversely, if the bit strikes a hard area which offers less resistance to the driving force of the bit motor, the reactive torque in the drill string will decrease and the rotation of the rotary table will slow down or stop completely. The operator can readily balance the system by lowering the drill string and hence increase the weight load on the bit until the table again begins to rotate slowly, thereby indicating that the system is in balance. Of course, the operator may wish to readjust the brake to a new setting, although this may not be required until after some time and possibly a change of a worn out bit. In other words, the operator may elect to leave the setting for the softer formations he previously encountered, and may encounter again, knowing that the brake is set so as to provide an adequate margin of safety.

The instant invention thus effectively provides a ground speed governor for the drill bit. The drill bit motor is relieved of excess pressure by the brake slippage and strain on the inner shafts of the motor is prevented from becoming excessive. The drill hole is kept in condition as to cutting accumulations and is not subject to a cumulative series of events which might otherwise escalate the drilling problems in rapid succession. There is less danger of the drilling fluid channeling in the annulus or a stuck drill string since the slow reverse turning of the drill string while drilling tends to prevent these problems. In addition, if the operator finds a sudden variation in reverse torque in the drill string without an apparent change in the nature of the cuttings discharged at the top of the annulus, it would be indicative that the drill direction is changing or a sloughing of the hole sides is taking place, and corrective measures must be taken to insure a straight hole. Thus, in most situations, the operator is given a visual warning that corrective action is required and, by taking such action, time loss, wasted fuel, and wear and tear on the equipment, particularly the down-hole motor, can be averted. The danger of plugging the hole or bit, or balling the bit, is greatly reduced and the operator can circulate the driving fluid indefinitely without flopping the bit off bottom at high speed, as is generally done when breakdowns in other equipment cause drilling stoppage. When the bit is off bottom and rotating at high speed, the bit will be dulled and caused to lose gauge size by side wear. In contrast, the present invention enables the operator to firmly set the bit on the bottom and, by releasing the brake or allowing the brake to drag and the bit to turn slowly, bit damage can be avoided while maintaining the condition of the walls of the well bore to prevent caving and lost circulation to formations.

Numerous modifications can be made in the invention without departing from its spirit and purpose. In particular, the braking mechanism is susceptible to numerous modifications and variations, the critical consideration being the provision of means which will enable the driller to adjust and control the rotation of the drill string in response to reactive torque developed in the string by the drill bit motor, the mechanism also affording the driller a visually perceptible indication of variations in the braking action.

One such modification is diagrammatically illustrated in FIG. 3 wherein the braking mechanism comprises an hydraulic pump operatively connected to the kelly, the pump effectively serving as an hydraulic braking mechanism. Thus, the braking mechanism may comprise a housing 29 having jaws 30 adapted to be detachably engaged about an elongated annular bushing a similar to the annular bushing 15, the jaws thus serving as a lateral support bearing coacting with the previously described hanger 19 and cable 20 to support the housing 29 which mounts a pump 31, which may be a vane, gear or piston type pump. Another type which may be employed is a helical gear pump marketed under the trademark MOYNO by Robbins & Myers, Inc. of Springfield, Ohio, U.S.A. The conventional MOYNO pump comprises a fixed element or stator having internal helical threads and a rotor element received within the stator and having one less helical thread than the stator. When motive power is applied to the rotor, a series of continuously moving pumping pockets is formed between the rotor and stator which will draw a liquid through the device. One form of such pump is illustrated in Moineau U. S. Pat. No. 2,505,136.

In accordance with the invention, the rotating element or rotor 32 of pump 31 is provided with a sprocket 33 engaged by a chain 34 which passes around a sprocket 35 operatively connected to the elongated bushing 15a, preferably through an overrunning clutch, indicated at 36, which is operable by the bushing in one direction only so that the kelly will drive the sprocket only when the kelly is rotating in response to reactive torque in the drill string. Thus, the sprocket 35 will rotate with the kelly in response to the reactive torque of the drill string and, in so doing, will drive the rotor 32 of the pump. Suitable stop means such as snap-rings or bearings, indicated generally at 37, will be provided to maintain the bushing 15a in alignment with the jaws 30 as well as with the sprocket 35, yet permitting the kelly to freely move longitudinally with respect to the bushing and braking mechanism as the drill string is raised and lowered by the draw works.

Rotation of the pump rotating element or rotor 32 will cause hydraulic fluid to be withdrawn from the supply tank 38 through conduit 39, the fluid being discharged from the pump for return to the supply tank through conduit 40. The desired braking effect is achieved by providing an adjustable choke valve 41 in conduit 40 which returns the hydraulic fluid to the supply tank.

With the arrangement just described, the hydraulic pump effectively serves as a braking mechanism, the braking force being adjustable by controlling the return flow of hydraulic fluid to the supply tank, restriction of the flow of fluid to the supply tank creating a back-pressure effective to retard or restrain rotation of the rotor 32 and thereby restrain rotation of the kelly 5 and the drill string connected thereto.

If necessary, it is also within the spirit and scope of the invention to provide a booster pump to increase the back-pressure resisting rotation of the rotating element 32. Such arrangement is diagrammatically illustrated in FIG. 5 wherein a booster pump 42 works in opposition to the return flow of fluid through conduit 40, a relief valve 43 acting to control the output of booster pump 42 so that it will either oppose return flow of hydraulic fluid through conduit 40 or be returned to the supply tank 38. When the booster pump is in use, the choke valve 41 is not required, although it may be retained in the system for use when the booster pump is not being operated.

FIG. 4 illustrates another modification of the invention wherein the braking mechanism is operatively connected to the rotary table 6 rather than to the kelly itself. Thus, the bevel gear 14 is connected to a drive shaft 44 adapted to be driven by prime mover 45 acting through gear box 46. A clutch 47 is provided by means of which the drive shaft may be disconnected from the prime mover to permit the rotary table to be free moving in response to the reactive torque developed in the drill string. A sprocket 48 is mounted on the drive shaft intermediate the bevel gear 14 and clutch 47, the sprocket 48 being engaged by a chain 49 passing around a sprocket 50 mounted on the rotor 51 of a pump 52 which, preferably, will comprise a MOYNO helical gear pump of the type previously described, although other forms of pumps may be employed. In this instance, the pump has an inlet conduit 53 positioned to withdraw drilling mud from the supply source 13, the return conduit 54 being provided with a choke valve 55 to restrict the return flow of fluid and hence create a back-pressure on the rotor of the pump which, acting through sprocket 50, chain 49, sprocket 48, drive shaft 44 and bevel gear 14, eflectively resists and retards rotation of the rotary table 6.

The foregoing modifications are illustrative of various braking mechanisms which may be employed. it should be evident that the braking pump 31 of the embodiment illustrated in FIG. 3 could be operated with drilling mud; conversely, the pump 52 of the FIG. 4 embodiment could be operated with hydraulic oil from a suitable source of supply. Alternatively, if an adequate source of water is available, water pressure could be utilized to operate the braking pumps, or where a positive displacement pump is employed, it may be pneumatically controlled. Other fonns of braking mechanism also may be employed, as for example, an electro-magnetic brake engageable with either a bushing on the kelly, such as the bushing 15, or with a drive shaft, such as the shaft 44, driving the rotary table 6. Similarly, a power swivel may be connected to the upper end of the kelly 5, the power swivel being arranged to resist the reactive torque developed in the drill string and kelly by the drill bit motor. A power sub could also be employed for such purpose, although currently availablepower subs are generally too small for such usage, although they could be used for shallow drilling operations or for heavier duty installations if redesigned to develop additional power.

Any of the braking mechanisms in which a clamping force is applied to the bushing on the kelly may be provided with a drum which will operate only in the reverse direction as an overrunning clutch, thereby enabling the operator to turn the rotary table in one direction. With such arrangement, the operator can rotate the table if operating conditions do not require the braking action. At the same time, the braking mechanism is available should it be required. In addition, the presence of an overrunning clutch would serve as a safety mechanism in the event of the accidental powering of the table while the brakingmechanism is in place.

Situations may also be encountered wherein, due to the depth of the hole and the length of the drill string, or due to a crooked hole, the drill string will bind in the hole. Such binding can be effectively overcome by providing stabilizers on the sections of drill pipe, such stabilizers being of known construction and of the type wherein the pipe is free to rotate within the stabilizers which, in effect, act asbearings for the rotating pipe.

The instant invention also lends itself to the use of sensing devices and servo-mechanisms to sense and interpret variations in drill string torque and correlate adjustment of the draw works and driving fluid pressure to achieve optimum operating conditions. Irrespective of the mode of control, the basic consideration remains the development of maximum power of thedrill bit motor, which is the product of speed and torque. Desirably, the down-hole motor will be operated constantly, when drilling, at its maximum rating in continuous torque output. The present-invention enables the driller to readily monitor and control the torque output of the downhole motor, and also may readily give the geologist exact locations of formation changes indicated by the sensitive changes in the reactive torque as they take place at certain depths and which are more immediately noticeable than variations in penetration rate or change in the nature of returned cuttings in the mud flow.

The embodiments of the invention in which an exclusive propertyor privilege is claimed are defined as follows:

1. In rotary well drilling apparatus wherein a string of drill pipe is operatively connected at its upper end to a polygonal kelly slidably journaled in a rotary table, wherein means are provided to raise and lower said drill string, wherein a motor is secured to the lowermost end of said drill string, and wherein a drill bit is connected to and driven by said motor, said drill bit motor, when drivingsaid drill bit, acting to develop reactive torque in said drill string to cause it to rotate in the direction opposite to the direction of rotation of said drill bit, the improvement which comprises mounting said rotary table to be freely rotatable by said drill string in the direction of rotation of said. drill string, and adjustable braking means operatively connected to said drill string, said braking means comprising an hydraulic pump having an inlet side and an outlet side, conduit means connected to the outlet side of said pump for discharging hydraulic fluid therefrom, and a choke valve in said discharge conduit means for adjusting the braking force applied by said braking means, whereby said braking means may be adjusted to control rotation of said drill string in response to variations in the reactive torque developed in the drill string by said drill bit motor.

2. The rotary well drilling apparatus claimed in claim 1 wherein said braking means engages said kelly and is operatively connected to said drill string through said kelly.

3. The rotary well drilling apparatus claimed in claim 2 wherein a bushing surrounds said kelly, said bushing being non-rotatably mounted with respect to said kelly but freely movable lengthwise thereof, said braking means being engageable with said bushing.

4. The rotary well drilling apparatus claimed in claim 3 including means non-rotatably mounting said braking means relative to said kelly.

5. The rotary well drilling apparatus claimed in claim 1 including means for driving said rotary table, said braking means being operatively connected to said drill string through said kelly, said rotary table, and said rotary table drive'means.

6. The well drilling apparatus claimed in claim 5 wherein said rotary table drive means includes a prime mover and clutch means for engaging and disengaging said prime mover, whereby when said prime mover is disengaged, said rotary table is free for rotation by said drill string.

7. The well drilling apparatus claimed in claim 1 wherein said hydraulic pump comprises a helical gear pump having a rotor and a stator, the rotor of said pump being operatively connected to said drill suing for rotation therewith.

8. The rotary well drilling apparatus claimed in claim 7 wherein the rotor of said helical gear pump is connected to said kelly.

9. The well drilling apparatus claimed in claim 7 including drive means for rotating said rotatable table, the rotor of said helical gear pump being connected to said rotary table drive means.

10. A method for governing the operation of a down-hole drill bit motor in a well drilling rig wherein a string of drill pipe is operatively connected at its upper end to a polygonal kelly slidably joumaled in a rotary table, wherein a drill bit is connected to and driven by said down-hole motor at a predetermined speed, and wherein means are provided to raise and lower said drill string to vary the weight load exerted on said drill bit by said drill string, comprising the steps of:

lowering said drill string to cause said drill bit to contact the bottom of the hole being drilled, rotating said drill bit at a predetermined rate of rotation, said drill bit motor, when driving said bit, acting to develop reactive torque in said drill string to cause said drill string to rotate in the direction opposite to the direction of rotation of said drill bit, applying a braking force to said drill string in proportion to the reactive torque developed in the drill string by said drill bit motor, said braking force being at least sufficient to retard the rotation of the drill string to the extent that it will rotate at an essentially uniform slow rate under a weight load on the drill bit effective to permit the drill bit motor to rotate the drill bit at said predetermined rate, and

selectively elevating the drill string to lighten the weight load on the drill bit upon an increase in the reactive torque developed in the drill string by said drill bit motor, as evidenced by an increase in the rate of rotation of said drill string, and lowering the drill string to increase the weight load on the bit when the torque developed in the drill string by the drill bit motor decreases, as evidenced by a decrease in the rate of rotation of said drill string, the variation in weight load on the drill bit being sufficient to effectively reestablish rotation of said drill bit at said predetermined rate, as indicated by rotation of said drill string at an essentially uniform slow rate of rotation in the direction opposite to the direction of rotation of said drill bit under the applied braking force.

11. The method claimed in claim 13 including the step of elevating the drill string to lighten the weight load on the drill bit upon an increase in the reactive torque developed in the drill string by said drill bit motor, as evidenced by an increase in the rate of rotation of said drill string, and lowering the drill string to increase the weight load on the bit when the torque developed in the drill string by the drill bit motor decreases, as evidenced by a decrease in the rate of rotation of said drill string, the variation in weight load on the drill bit being sufficient to effectively reestablish rotation of said drill bit at said predetermined rate, as indicated by rotation of said drill string at an essentially uniform slow rate of rotation in the direction opposite to the direction of rotation of said drill bit under the applied braking force.

12. The method claimed in claim 10 including the step of selectively varying the braking force applied to said drill string to assist in retarding rotation of said drill string in a direction opposite to the direction of rotation of said drill bit motor.

l l I l 

1. In rotary well drilling apparatus wherein a string of drill pipe is operatively connected at its upper end to a polygonal kelly slidably journaled in a rotary table, wherein means are provided to raise and lower said drill string, wherein a motor is secured to the lowermost end of said drill string, and wherein a drill bit is connected to and driven by said motor, said drill bit motor, when driving said drill bit, acting to develop reactive torque in said drill string to cause it to rotate in the direction opposite to the direction of rotation of said drill bit, the improvement which comprises mounting said rotary table to be freely rotatable by said drill string in the direction of rotation of said drill string, and adjustable braking means operatively connected to said drill string, said braking means comprising an hydraulic pump having an inlet side and an outlet side, conduit means connected to the outlet side of said pump for discharging hydraulic fluid therefrom, and a choke valve in said discharge conduit means for adjusting the braking force applied by said braking means, whereby said braking means may be adjusted to control rotation of said drill string in response to variations in the reactive torque developed in the drill string by said drill bit motor.
 2. The rotary well drilling apparatus claimed in claim 1 wherein said braking means engages said kelly and is operatively connected to said drill string through said kelly.
 3. The rotary well drilling apparatus claimed in claim 2 wherein a bushing surrounds said kelly, said bushing being non-rotatably mounted with respect to said kelly but freely movable lengthwise thereof, said braking means being engageable with said bushing.
 4. The rotary well drilling apparatus claimed in claim 3 including means non-rotatably mounting said braking means relative to said kelly.
 5. The rotary well drilling apparatus claimed in claim 1 including means for driving said rotary table, said braking means being operatively connected to said drill string through said kelly, said rotary table, and said rotary table drive means.
 6. The well drilling apparatus claimed in claim 5 wherein said rotary table drive means includes a prime mover and clutch means for engaging and disengaging said prime mover, whereby when said prime mover is disengaged, said rotary table is free for rotation by said drill string.
 7. The well drilling apparatus claimed in claim 1 wherein said hydraulic pump comprises a helical gear pump having a rotor and a stator, the rotor of said pump being operatively connected to said drill string for rotation therewith.
 8. The rotary well drilling apparatus claimed in claim 7 wherein the rotor of said helical gear pump is connected to said kelly.
 9. The well drilling apparatus claimed in claim 7 including drive means for rotating said rotatable table, the rotor of said helical gear pump being connected to said rotary table drive means.
 10. A method for governing the operation of a down-hole drill bit motor in a well drilling rig wherein a string of drill pipe is operatively connected at its upper end to a polygonal kelly slidably journaled in a rotary table, wherein a drill bit is connected to and driven by said down-hole motor at a predetermined speed, and wherein means are provided to raise and lower said drill string to vary the weight load exerted on said drill bit by said drill string, comprising the steps of: lowering said drill string to cause said drill bit to contact the bottom of the hole being drilled, rotating said drill bit at a predetermined rate of rotation, said drill bit motor, when driving said bit, acting to develop reactive torque in said drill string to cause said drill string to rotate in the direction opposite to the direction of rotation of said drill bit, applying a braking force to said drill string in proportion to the reactive torque developed in the drill string by said drill bit motor, said braking force being at least sufficient to retard the rotation of the drill string to the extent that it will rotate at an essentially uniform slow rate under a weight load on the drill bit effective to permit the drill bit motor to rotate the drill bit at said predetermined rate, and selectively elevating the drill string to lighten the weight load on the drill bit upon an increase in the reactive torque developed in the drill string by said drill bit motor, as evidenced by an increase in the rate of rotation of said drill string, and lowering the drill string to increase the weight load on the bit when the torque developed in the drill string by the drill bit motor decreases, as evidenced by a decrease in the rate of rotation of said drill string, the variation in weight load on the drill bit being sufficient to effectively reestablish rotation of said drill bit at said predetermined rate, as indicated by rotation of said drill string at an essentially uniform slow rate of rotation in the direction opposite to the direction of rotation of said drill bit under the applied braking force.
 11. The method claimed in claim 13 including the step of elevating the drill string to lighten the weight load on the drill bit upon an increase in the reactive torque developed in the drill string by said drill bit motor, as evidenced by an increase in the rate of rotation of said drill string, and lowering the drill string to increase the weight load on the bit when the torque developed in the drill string by the drill bit motor decreases, as evidenced by a decrease in the rate of rotation of said drill string, the variation in weight load on the drill bit being sufficient to effectively reestablish rotation of said drill bit at said predetermined rate, as indicated by rotation of said drill string at an essentially uniform slow rate of rotation in the direction opposite to the direction of rotation of said drill bit under the applied braking force.
 12. The method claimed in claim 10 including the step of selectively varying the braking force applied to said drill string to assist in retarding rotation of said drill string in a direction opposite to the direction of rotation of said drill bit motor. 